Nuclear transfer to prevent maternal transmission of mitochondrial DNA disease

Two new techniques to prevent diseases of maternally transmitted mitochondrial DNA—maternal spindle transfer and pronuclear transfer—have prompted a public consultation by the Human Fertilisation and Embryology Authority (HFEA) in the United Kingdom.1 2 3 After the announcement of the consultation, much of the comment in the press focused on “three parent embryos” as if they were a novelty.4 They are not, and such red herrings serve only to cloud the debate.

About one in 400 people have a maternally inherited pathogenic mutation of mitochondrial DNA. Mutations may cause no symptoms or may present at any age with problems such as developmental regression, deafness, blindness, neuropathy, diabetes, or cardiomyopathy. Mitochondrial DNA is maternally inherited because mitochondria are located in the cytoplasm, and the sperm contributes almost no cytoplasm to the fertilised egg. Many of these diseases are heteroplasmic—that is, mitochondria with mutant and normal DNA coexist in the same patient; low doses of mutant DNA cause mild symptoms and high doses cause severe symptoms. If heteroplasmic women transmit high doses of mutant mitochondrial DNA to their children,5 these children are severely affected. Homoplasmic women, whose mitochondria all have identical DNA, transmit 100% mutant …